The long-term objective of this research project is to obtain a better understanding of the molecular mechanisms governing the first step in tumor cell dissemination, namely motility. To accomplish this goal it is proposed to define the biological function and mechanism of action of an autocrine motility factor (AMF) and its receptor (gp78). AMF was originally identified in 1986, as a proteinaceous molecule that stimulated the locomotion of self-producing cells, hence its name. Until recently, its molecular identity had proved extremely elusive. We have found during this granting period (1996, partial protein sequencing, 1998 molecular cloning), that AMF was previously identified as three different proteins, i.e., neuroleukin (NLK), phosphohexose isomerase (PHI) and a maturation factor (MF), and each was independently implicated in cell motility and mitogenicity. AMF/NLK/PHI/MF exerts its signal through ligation to a cell surface receptor (gp78) whose predicted secondary structure displays seven putative helical transmembrane domains, a structural feature shared by all members of the G-protein-coupled receptor class of transmembrane proteins. We have shown that the expression levels of both receptor and ligand determine cell motility in vitro and serve as prognostic markers for tumor progression in vivo. On the basis of these observations, we set the following four specific aims in this renewal application: Specific Aim 1) To study the regulation of AMF gene expression in normal and high- and low-metastatic cancer cells; Specific Aim 2) To study the structural-functional relationship of AMF activity; Specific Aim 3) To establish the secretory pathway of AMF; Specific Aim 4) To study the consequences of AMF/receptor-binding leading to differential morphological changes, membrane ruffling and cell motility in high- and low-metastasizing cancer cells. It is expected that the accomplishment of these aims will help in obtaining our goal of unveiling how the autocrine loop of AMF signaling through its receptor alters cellular properties, and how it can be exploited for therapeutic interventions of invading cancer cells.